Rotational speed measurement device for rotating missiles

ABSTRACT

A spin rate measurement device for rotating missiles. Preferably, three micromechanical spin rate sensors whose three spatial axes are aligned at right angles to one another, each of which is designed to be excited, read and reset capacitively, are arranged on a single platform that can be rotated by means of a servo loop for rotation decoupling. The spin rate measurement device is distinguished by high bias and scale factor stability that can be checked at any time.

BACKGROUND

1. Field of the Invention

The present invention relates to rotation or spin measurements forrotating missiles. More particularly, this invention pertains toapparatus for rotation or spin measurement for stabilization of rotatingmissiles.

2. Description of the Prior Art

The ability to measure and process high roll spin rates of rotatingmissiles (e.g., 5000 to 10,000°/s) is a fundamental requirement of aflight attitude stabilization device for maintaining specific roll,pitch and azimuth angles with respect to an initial position.

The options for solving this fundamental problem are briefly outlinedbelow:

(a) spin-stabilized two-axis integrating gyro systems (i.e., cold gas orpowder gyro arrangements);

(b) optical gyro systems having high spin rate capacity and scale factorstability, (e.g., ring laser or fiber optic gyros);

(c) vibration gyroscopes based on the Coriolis principle in whichsymmetrical oscillator structures oscillate within a plane subject to aslittle damping as possible and provide high scale factor of accuracy.

The first two approaches (“a” and “b”) satisfy the technicalrequirements while incurring excessive unit costs. In the traditional,mechanical integrating solution (proposal a), the gyro systems areconstructed from mechanical parts which, from the beginning, offereconomies when relatively large quantities are employed. This solutionsuffers the substantial disadvantage that functional tests prior tomissile launch are possible only to a limited extent. In practice, suchtests can only be carried out on a sample test basis because it is toorisky due to particles to renew or replace the gas or powder reservoir.This is possible only at a considerable cost and this solution suffersunder limited reliability because of the testability restrictions.

The bias of optical gyro systems according to proposal b can be readilychecked, even after long storage times. High scale factor accuracy isrequired to measure high spin rates and can only be checked withdifficulty. Expensive tests on rotating tables are unacceptable afterthe missile has been stored for a long period of time. Proposals existfor monitoring the scale factors of ring lasers and fiber optic gyroswithin systems, with accuracy requirements of, e.g., 0.02%, over storagetimes of up to 20 years. However, unit costs for optical gyros becomeunacceptably high, even when the fact that optical components andassemblies are becoming ever cheaper due to newer production methods istaken into account.

Initially, a vibration gyroscope according to proposal “c” would appearto offer a highly promising solution to the problem. Induced vibrationin an ideal resonator with high Q-factor retains its inertialorientation even at high roll rates. Thus, in theory, an ideal spin-rateintegrating gyroscope system is possible. However, known resonatorscannot, in fact, be produced with such ideal characteristics. Tuningfork oscillators, as well as ring or circular oscillator systems, forexample, have a number of oscillation modes and natural frequencies thatmust be matched to one another. Thus, ring oscillator configurations,for example, do not maintain their inertial orientations due to theBryan factor. Theoretically, an output oscillation angle of about 60%with respect to the input angle is obtained. However, the 60%discrepancy depends upon the actual natural modes and respectivemechanical coupling. Should they change, due to external vibration orshocks during storage, the scale factor then changes. As a result the0.02% accuracy requirement cannot be satisfied over a relatively longstorage period.

In the case of double tuning fork oscillators, the Bryan factor isvirtually 100%. Discrepancies of about 1.3% must be taken into account,so that the required scale factor stability of 0.02% is virtuallyimpossible to achieve after storage for up to 20 years. Furthermore,checking involves major practical difficulties.

A further problem of both vibration gyroscope concepts results fromunavoidable damping. In practice, to insure operation as a spin rateintegrating gyroscope, damping must be electronically overcome (at leastfor the two modes employed). Constant excitation is required for theinitial vibration mode. Damping for the other oscillation mode must beovercome, for example, by electronic torquers, without forcing suchoscillation mode absent Coriolis forces. If the damping cannot becorrectly overcome, considerable errors will occur in integratinggyroscopes, perhaps sufficient for the two oscillation modes to becomeunstable.

To compensate for temperature-dependent gas damping, vibrationgyroscopes would have to be operated in a vacuum, particularly forminiaturized designs. It is, however, difficult and expensive tomaintain a stable small volume vacuum over long storage times (up to 20years).

SUMMARY AND OBJECTS OF THE INVENTION

It is therefore an object of the present invention to provide a spinrate measurement device for stabilizing the track attitude of rotatingmissiles.

It is a further object of this invention to achieve the above objectwhile obtaining high bias and scale factor stability in a missile thathas been stored for a long time.

It is yet another object of the present invention to achieve theforegoing objects with a device having good testability and low unitcosts.

The present invention achieves the above and other objects by providinga spin rate measurement device for rotating missiles. Such deviceincludes at least one micromechanical spin rate sensor. The sensor ismounted on a platform. One axis of the platform can be driven in acontrolled manner by means of a servo loop for rotation decoupling ofthe spin rate sensor.

The preceding and other features of the invention will become furtherapparent from the detailed description that follows. Such description isaccompanied by a set of drawing figures. Numerals of the drawingfigures, corresponding to those of the written description, point to thefeatures of the invention with like numerals referring to like featuresthroughout both the written text and the drawing figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded perspective view of a spin rate measurement devicein accordance with the invention;

FIG. 2 is a block diagram for illustrating the electronics of the spinrate measurement device; and

FIG. 3 illustrates a micromechanical spin rate sensor, the figureincorporating the associated drive, reading and resetting electronics.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 is an exploded perspective view of a spin rate measurement devicein accordance with the invention. It includes a pot-like housing 1 witha cover 2, in which a rotor 9 (platform), designed as a drum-like hollowbody, is mounted for rotation by supporting ball bearings 5. Threemicromechanical spin rate sensors (not shown in FIG. 1) are arranged ina space inside the rotor 9. The measurement axes of the sensors are eachfixed and aligned with one spatial direction. A printed circuit board 6(“interface board”) is connected to the housing 1. The electronics forthe external interface (explained in greater detail below with referenceto FIG. 2) is located on it, while the electronic assemblies for thedrive, resetting, amplifier and processor electronics of the threemicromechanical spin rate sensors, as well as the angle pick-off and thedrive for the rotor (platform) 9, are located on a second printedcircuit board (“processor board”) located inside the rotor 9 (notillustrated). A spin angle coder, including optical reading of the spinangle of the rotor 9, is identified by the reference 3, while slip rings4 are employed for voltage transmission. Data transmission is preferablyperformed optically (not illustrated). The motor for driving the rotor 9is also not shown in FIG. 1.

FIG. 2, a block diagram for illustrating the electronics of the spinrate measurement device, shows all the electronics forthree-micromechanical gyros on the stabilized single-axis platform 9.The central block of the electronics is a processor 10 (digital ASIC)which operates both the control loops for the micromechanical spin ratesensors 30 and their associated electronics 12, and a driver ASIC.13.The driver ASIC 13 reads the optical spin angle coder 3 and controls therotor rotation via a motor 14 and a power stage 15 so that rotorrotation compensates for .the spinning of the missile. All data arepassed on via a further driver ASIC 17, using optical data transmission16. The external voltage supply is passed via the slip rings 4 and isprocessed internally in the block 18.

FIG. 3, illustrates a micromechanical spin rate sensor incorporating theassociated drive, reading and resetting electronics. The figure showsthe principle of design of a micromechanical spin rate sensor inaccordance with the invention based on the Coriolis principle. As can beseen in the figure, the micromechanical spin rate sensor 30 in principlecomprises two oscillators in the form of plates, arranged in two levels,like layers, one above the other, that can be excited in antiphase andcapacitively excited to oscillate at right angles to their respectiveplate levels, in which case the drive 31 acts in the region of a verynarrow drive gap 32. This leads to comparatively large oscillationamplitudes which are read at the right-hand (preferably free) end of thetwo oscillators at 33 and transmitted, via a preamplifier 34, to a phasecomparator and synchronous demodulator 35, whose output signal is passedvia an A/D converter 36 to a data bus 37 to which a processor 46 anddrive electronics 38 are connected. The drive electronics 38 producesthe driver pulses for the drive 31 and the resetting pulses for a resetdriver 39 that capacitively resets the spin rate in the central region40 of the micromechanical spin rate sensor 30. The capacitive spin ratereading for controlling the resetting pulses is accomplished via top andbottom plate pairs in the drive range (i.e., on the left-hand side ofthe spin rate sensor 30). The read signals are passed via a preamplifier41 to a further synchronous demodulator 42 that is fed by the samesynchronization clock as the synchronous demodulator 35. Its outputsignal is likewise passed to the A/D converter group 36 and, from there(via the bus 37) to the processor 46. As shown, individual electronicassemblies, as well as the drive electronics 38, the two drivers 31 and39 and the assemblies 34, 41, 42 and 35, 36 can be designed asapplication-specific ASICs (i.e. as an integrated circuit). The measuredspin rate is output via the serial interface 43. Open or reset systemsmay be used as micromechanical spin rate sensors for the envisagedapplication, such as those described, for example, in the publishedInternational Patent Application WO 96/38710, oscillator structuresbased on the Coriolis principle, have at least two layers and can beexcited and read capacitively, preferably with a resetting capabilitywhich likewise acts capacitively.

The combination according to the invention of micromechanical spin ratesensors with electromechanical rotation decoupling offers the followingfunctional and economic advantages:

Three identical gyroscopes can be accommodated on a single-axis platformwithout any problem;

The principle of the solution results in the requirements for biasstability being reduced to about 0.33°/s, which, as a rule, aresufficient;

Scale factor requirements are reduced from 0.02% to 1% due tocompensation by the rotating platform;

In comparison to solution approach (a) with two mechanical gyro systemseach having three axes, only a single, single-axis mechanical platformis required; and

All functions can be completely tested during or at the end of a storagetime, so that the risk of functional failure is minimized.

While this invention has been described with reference to itspresently-preferred embodiment, it is not limited thereto. Rather, it islimited only insofar as it is described by the following set of patentclaims and includes within its scope all equivalents thereof.

What is claimed is:
 1. A spin rate measurement device for track/attitudestabilization of rotating missiles, comprising, in combination: a) threemicromechanical spin rate sensors whose three axes are aligned at rightangles to one another; b) said sensors being mounted together on asingle axis platform which can be installed on the missiles; and c) oneaxis of said platform can be rotated by means of a servo loop forrotation decoupling of said spin rate sensors.
 2. A spin ratemeasurement device as defined in claim 1 wherein: a) said spin ratesensors comprise oscillator structures based on the Coriolis principle;b) each said sensor.includes at least two layers; and c) said sensorscan be capacitively excited and read.
 3. A spin rate measurement deviceas defined in claim 2 wherein said spin rate sensors comprise oscillatorstructures that can be capacitively reset.
 4. A spin rate measurementdevice as defined in claim 1, characterized in that electronics of thespin rate sensors, a rotor pick-off and a rotor drive are combined inthe interior of said platform.